During the current funding period, the principal investigator has identified a population of primitive hematopoietic progenitors from human bone marrow using a combination of cell sorting and long-term bone marrow culture (LTBMC) techniques. He hypothesizes that this cell population can be used to study in vitro the important, but poorly understood, interactions of normal primitive hematopoietic progenitors with bone marrow stroma, and changes in these interactions which may occur in malignantly transformed progenitors from bone marrow of patients with chronic myelogenous leukemia (CML). 1) Mechanisms underlying the observed avid adhesion of normal primitive progenitors of bone marrow stroma will be explored. Primitive progenitors will be panned on surfaces coated with irradiated normal bone marrow stroma, fibronectin, and other purified extracellular matrix (ECM) adhesion proteins or their subcomponents. Adhesion blocking assays will be performed to identify specific ECM protein binding domains and progenitor cell adhesion receptors. More committed progenitor populations from normal bone marrow (observed to have diminished adhesion to stroma) will also be tested and results compared. These experiments may identify adhesion mechanisms necessary for early developmental regulation of normal primitive progenitors in bone marrow stroma and changes in adhesion properties of differentiating progenitors associated with changing migratory capacity. 2) Mechanisms underlying the observed diminished adhesion of primitive progenitors from CML bone marrow to normal bone marrow stroma will be explored using similar adhesion and adhesion blocking assays. Specific ECM protein binding domains and progenitor cell receptors implicated in adhesion of CML progenitors will be identified and compared to those implicated in adhesion of normal primitive progenitors. These experiments may identify mechanisms underlying differences in progenitor adhesion associated with malignant transformation, and which explain in part abnormal differentiation and migratory capacities characteristic of CML. 3) Experiments will be designed to separate benign and malignant primitive progenitor subpopulations coexisting in bone marrow and some CML patients by capitalizing on their different capacities to adhere to normal bone marrow stroma or its ECM components. Viability of separated subpopulations will be assessed by LTBMC, and the benign or malignant nature of progenitor subpopulations determined by cytogenetic and molecular genetic techniques. These experiments may select benign, viable primitive progenitors from CML bone marrow which can be used in subsequent autologous bone marrow transplant therapy of this lethal disease.